Bipolar transistors (BJT)

Haiben has supplied electronic components from Shenzhen since 2013, working with purchasing teams and hardware engineers who need clear specifications and dependable availability. Our transistor programme covers the bipolar transistor families that most boards still rely on — small-signal NPN and PNP parts, pre-biased digital types, Darlington and composite devices — alongside a complementary MOSFET range. This page sets out what we stock, how each family is normally applied, and what to confirm before you release a part to production.

The BJT range at a glance

The bipolar transistor remains a default choice for switching, amplification and simple bias networks, and the range we hold reflects that: small-signal SMD types for dense boards, through-hole parts for prototyping and legacy layouts, and pre-biased devices that remove discrete resistors from the bill of materials. Our NPN & PNP transistors category groups these by polarity and package, and the own-brand Weforsemi line is operated by our wholly-owned subsidiary, so the parts below are supplied under that brand rather than as third-party stock.

Package coverage runs from TO-92 through SOT-23 and SOT-523 down to SOT-723 and DFN-style composite packages. That spread matters in practice: the same electrical function is often needed at three different assembly densities, and selecting by package first usually narrows the choice quickly.

NPN, PNP and the packages stocked

Small-signal SMD devices include the VC3904TB, an NPN in SOT-523, and the VC3906B, a PNP in SOT-23 — a complementary pair pattern that suits push-pull stages and level shifting. For slightly higher current, the VC8050X-0.3A (SOT-23, NPN) and the VCSS8050B-1.5A (SOT-23, NPN, 300 mW class) sit in the same package footprint family.

Through-hole users have the VC2N4401Z (TO-92, NPN, 600 mA) and the VC2N3906Z (TO-92, PNP, 40 V). For very small SMD switching and amplification duties, the VC2SC4617F is an NPN in SOT-523 rated 150 mW.

Digital and composite types

• VC143ZEF — NPN digital transistor, SOT-523
• VC143ZME — NPN digital transistor, SOT-723, 150 mW
• VC5853DCJ — MOSFET-Schottky composite transistor, DFNWB3x2-8L, Vrrm 20 V
• VCMNT32D — PNP power transistor with N-MOSFET, DFNWB2x2-6L, ultra-low collector-emitter saturation voltage and high DC current gain

Digital, or pre-biased, transistors integrate the base resistor network inside the package, which saves board area and removes a resistor from the BOM. The Darlington and composite category covers devices that pair a bipolar stage with another element to raise gain or add a body-diode function.

BJT transistor roles in current designs

Despite the shift of many power paths to MOSFETs, the bipolar transistor still carries a lot of routine work. Typical roles include:

• Signal switching: driving relays, LEDs and small loads where a few hundred milliamps is enough.
• Amplification: low-noise and small-signal gain stages, especially with TO-92 and SOT-523 parts.
• Level shifting and interfacing: matching logic domains or buffering a sensor output.
• Biasing and current sources: reference and mirror circuits built from matched NPN or PNP pairs.
• Gate drive and pre-drive: composite types such as VCMNT32D handle the interface between control logic and a power stage.

Where a design already references common industry types, our 2N3904 / 2N3906 / S8050 cross reference helps map an existing part to a stocked equivalent before you commit a layout change.

Specifying transistors and checking pinouts

Start from the electrical requirement, not the part number: collector current, voltage rating, gain band, saturation voltage and power dissipation set the shortlist, and package then follows from board space and thermal expectations. For switching duty, check saturation voltage at the actual base drive you can supply; for amplification, check gain at the operating collector current rather than the headline figure.

One caution applies throughout. SOT-23 and SOT-523 transistor pin configurations vary between manufacturers, so the pinout must be confirmed against the datasheet for any named-original replacement. The same applies to pin-1 orientation on DFN-style composite packages. We recommend confirming pinout, polarity and package marking on the datasheet before releasing a part to production, even when the electrical specification appears to match exactly.

Frequently asked questions

Is a bipolar transistor the same as a BJT?

Yes. Bipolar junction transistor and bipolar transistor are two names for the same device family, and our listings use both terms interchangeably.

Do you supply third-party branded transistors?

The transistor and MOSFET models listed on this site are part of our own-brand Weforsemi line, operated by our wholly-owned subsidiary. We do not claim distribution authorisation for other manufacturers' brands.

Can I replace an existing part with a Weforsemi equivalent without a layout change?

Electrically similar parts often fit, but package pinout must be verified first. SOT-23 and SOT-523 pin configurations differ between manufacturers, so always confirm against the datasheet before substituting on an existing board.